How to add more editors
In this case, when a window shows 'Back to Previous', it means that you can press ctrl-up arrow and return to the non-focused layout. This view has been focused on the current active window with the ctrl-up arrow.

If you open a new file and it doesn't have the layouts liek you are used to using, sometimes you can get them back by reopening the file with 'Load UI' unchecked.